Audio amplifier



FIG. 1 is a perspective view of an audio amplifier as seen from the front, top and side;

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a top view thereof;

FIG. 5 is a bottom view thereof;

FIG. 6 is an opposite side view thereof; and,

FIG. 7 is a side view thereof.

The dotted line portions of the drawings represent environmental structure only and form no part of the claimed design. 

CLAIM The ornamental design for an audio amplifier, substantially as shown and described. 